Mutans streptococci have been implicated in the initiation of dental caries in humans. Streptococcus mutans have several virulence factors that allow the bacteria to accumulate within the dental biofilm and produce and tolerate the acids that cause dental caries. The ability of cariogenic mutans streptococci to accumulate in the dental biofilm is thought to be a consequence of the synthesis of glucans by glucosyltransferases, followed by the binding of the bacteria to these polymers via the cell-associated glucan binding proteins (Gbps). Biofilm development occurs in two distinct phases. During the first phase, bacterial surface proteins interact with host or bacterial products adsorbed on the tooth surface. In the second phase, a biofilm forms as bacteria accumulate by aggregation with the same or other species and produce an extracellular polysaccharide matrix.
Epitopes associated with these functions are thought to be primary targets for immunogenic attack, provided that the relevant sequences are located in molecular areas that can be accessible to antibody. Several mutans streptococcal proteins with glucan binding activity have been described (Russell, R. R., J. Gen. Microbiol., 112:197–201 (1979); Smith D. J. et al., Infect. Immun. 62:2545–2552 (1994); Sato, Y., et al., Infect. Immun., 65:668–675 (1997)). One of these components, glucan-binding protein-B (GbpB), has been shown to induce protective immune responses against experimental dental caries following systemic or mucosal immunization (Smith D. J. et al., Infect. Immun. 64:3069–3073 (1996) and Smith D. J. et al., Oral Microbiol. Immunol. 13:278–285(1998)). Furthermore, there is evidence that the expression of GbpB is directly related to biofilm formation (Mattos-Graner, R.O., et al., Infect. and Immun. 69(11) 6931–6941(2001)). However, use of the intact GbpB protein in a vaccine may induce immunity to irrelevant or unwanted epitopes.